It has been known that the glucose level in living tissue can be measured non-invasively by applying an electrode arrangement to the skin of a patient and measuring the response of the electrode arrangement to a suitable electric signal. Such a technique is described in WO 02/069791, the disclosure of which is enclosed herein in its entirety.
This type of device is equipped with an electrode arrangement for being applied to the specimen and a voltage-controlled oscillator as a signal source for generating an AC voltage in a given frequency range. The AC voltage is applied to the electrode arrangement. The response of the electrode arrangement, such as a voltage over the electrode arrangement depending on the dielectric properties of the tissue, is fed to a processing circuitry.
Even though this device is well able to monitor glucose, it needs careful calibration and must be operated under well-defined conditions in order to yield results of high accuracy.
The device of WO 02/069791 is one example of a device for measuring a parameter of living tissue. Similar types of devices can be used to measure other properties of the tissue that affect its response to an electric AC field; such as its dielectric constant, or an ion concentration.
Devices of this type should have high accuracy. In addition, in portable devices, low power consumption and low power supply voltages are desired.